|Publication number||US8004803 B2|
|Application number||US 12/281,803|
|Publication date||Aug 23, 2011|
|Filing date||Apr 17, 2008|
|Priority date||May 8, 2007|
|Also published as||US20100229580, WO2008137276A1|
|Publication number||12281803, 281803, PCT/2008/60612, PCT/US/2008/060612, PCT/US/2008/60612, PCT/US/8/060612, PCT/US/8/60612, PCT/US2008/060612, PCT/US2008/60612, PCT/US2008060612, PCT/US200860612, PCT/US8/060612, PCT/US8/60612, PCT/US8060612, PCT/US860612, US 8004803 B2, US 8004803B2, US-B2-8004803, US8004803 B2, US8004803B2|
|Inventors||Harold R. Schnetzka|
|Original Assignee||Johnson Controls Technology Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (56), Non-Patent Citations (3), Referenced by (3), Classifications (16), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This patent application claims the benefit of U.S. Provisional Patent Application No. 60/916,674, entitled VARIABLE SPEED DRIVE SYSTEMS AND METHODS, filed May 8, 2007, for which priority is claimed and the disclosure of which is hereby incorporated by reference.
The present application relates generally to variable speed drives. The application relates more specifically to systems and methods in variable speed drives having active converters with integral ground fault protection.
A variable speed drive (VSD) for heating, ventilation, air-conditioning and refrigeration (HVAC&R) applications may include a rectifier or converter, a DC link, and an inverter. Ground fault protection within a VSD can be implemented in various ways. One such method utilizes an external ground fault sensor (a single “zero sequence” current transformer and detection circuitry) that opens a set of relay contacts. The relay contacts may be connected to a shunt-trip device within a circuit breaker that opens the circuit breaker when energized. The circuit breaker is placed at the input power terminals of the VSD. Another ground fault protection method utilizes a molded case circuit breaker with a trip unit that incorporates a ground fault detection circuit. These units typically have a higher level of ground fault current trip as they typically utilize three current sensors, one per phase on a three-phase system, and sum the outputs to effectively sense the zero sequence/ground fault current. The integrated circuit breaker units are much more compact than earlier ground fault circuit breakers. However the level at which the ground fault current trip can be sensed is greater, and the accuracy of the sensed ground fault current is reduced, as a result of the three phase sensors. Another ground fault protection method utilizes motor current sensing means to shut down the inverter section of the VSD. This method fails to provide ground fault protection in the event of a ground fault occurring internally in the VSD. This method also fails to provide ground fault protection when there is a low impedance earth-referenced power feed and a ground fault occurs at the output of the VSD.
One embodiment of the present invention relates to a variable speed drive system configured to receive an input AC voltage at a fixed AC input voltage and provide an output AC power at a variable voltage and variable frequency. The variable speed drive includes a converter stage connected to an AC power source providing the input AC voltage, the converter stage being configured to convert the input AC voltage to a boosted DC voltage; a DC link connected to the converter stage, the DC link being configured to filter and store the boosted DC voltage from the converter stage; and an inverter stage connected to the DC link, the inverter stage being configured to convert the boosted DC voltage from the DC link into the output AC power having the variable voltage and the variable frequency. The variable speed drive also includes a ground fault protection system for interrupting fault current flowing to an input phase of the active converter, the ground fault protection system including at least one current sensor for sensing a ground fault on an input phase of the active converter, and a controller; wherein the active converter further includes at least two semiconductor switches for each power phase of the AC power source; each of the at least two semiconductor switches comprising a pair of reverse blocking IGBTs inversely connected in parallel, wherein each of the reverse blocking IGBTs is controllable by the controller to switch the RB IGBTs to a nonconductive state in response to a sensed ground fault current.
Another embodiment of the present invention relates to a ground fault protection system in an active converter for instantaneously interrupting a ground fault at an input phase of the active converter, using reverse blocking IGBTs in anti-parallel to controllably switch off fault current in response to a sensed fault.
VSD 28 receives AC power having a particular fixed line voltage and fixed line frequency from AC power source 26 and provides AC power to motor(s) 30 at a desired voltage and desired frequency, both of which can be varied to satisfy particular requirements. Preferably, VSD 28 can provide AC power to motor(s) 30 having higher voltages and frequencies and lower voltages and frequencies than the rated voltage and frequency of motor(s) 30. In another embodiment, VSD 28 may again provide higher and lower frequencies but only the same or lower voltages than the rated voltage and frequency of motor(s) 30. Motor(s) 30 is preferably an induction motor, but can include any type of motor that is capable of being operated at variable speeds. Motor 30 can have any suitable pole arrangement including two poles, four poles or six poles.
With regard to
For each motor 30 to be powered by VSD 28, there is a corresponding inverter 36 in the output stage of VSD 28. The number of motors 30 that can be powered by VSD 28 is dependent upon the number of inverters 36 that are incorporated into VSD 28. In one embodiment, there can be either 2 or 3 inverters 36 incorporated in VSD 28 that are connected in parallel to DC link 34 and used for powering a corresponding motor 30. While VSD 28 can have between 2 and 3 inverters 36, it is to be understood that more than 3 inverters 36 can be used so long as DC link 34 can provide and maintain the appropriate DC voltage to each of inverters 36.
Compressor 40 compresses a refrigerant vapor and delivers the vapor to condenser 42 through a discharge line. Compressor 40 can be any suitable type of compressor, e.g., screw compressor, centrifugal compressor, reciprocating compressor, scroll compressor, etc. The refrigerant vapor delivered by compressor 40 to condenser 42 enters into a heat exchange relationship with a fluid, e.g., air or water, and undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the fluid. The condensed liquid refrigerant from condenser 42 flows through an expansion device (not shown) to evaporator 44.
Evaporator 44 can include connections for a supply line and a return line of a cooling load. A secondary liquid, e.g., water, ethylene, calcium chloride brine or sodium chloride brine, travels into evaporator 44 via return line and exits evaporator 44 via supply line. The liquid refrigerant in evaporator 44 enters into a heat exchange relationship with the secondary liquid to lower the temperature of the secondary liquid. The refrigerant liquid in evaporator 44 undergoes a phase change to a refrigerant vapor as a result of the heat exchange relationship with the secondary liquid. The vapor refrigerant in evaporator 44 exits the evaporator 44 and returns to compressor 40 by a suction line to complete the cycle. It is to be understood that any suitable configuration of condenser 42 and evaporator 44 can be used in system 38, provided that the appropriate phase change of the refrigerant in condenser 42 and evaporator 44 is obtained.
HVAC, refrigeration or liquid chiller system 38 can include many other features that are not shown in
Each of the upper and lower switches 50 and 52 is comprised of two RB IGBTs 58, 56. An RB IGBT is capable of blocking voltages in the reverse as well as the forward direction. A first RB IGBT 58 is connected to an inverse or anti-parallel IGBT 56. Anti-parallel IGBT 56 is also an RB-type IGBT. Anti-parallel IGBT 56 can be controlled, e.g., during a precharge operation of DC link 34, to permit only small pulses of inrush current to reach DC link 34. Further, anti-parallel IGBT 56 can be controlled to conduct current in one direction at all times, similar to anti-parallel diode 54. RB IGBT 58 blocks a positive emitter-to-collector voltage that is approximately equal to the peak line-to-line voltage that appears across IGBT 58. The positive emitter-to-collector voltage remains blocked for as long as the conduction of anti-parallel IGBT 56 is delayed for the purpose of precharge. Commonly assigned U.S. Pat. No. 7,005,829 and U.S. Published Pat. App. No. 20060208685, No. 20060196203 & No. 20050122752, disclose various means to implement an active converter module to allow for precharging the DC link of a VSD or a parallel active harmonic filter, and the same are hereby incorporated by reference herein.
When a ground fault current is sensed by the VSD 28, both RB IGBTs 58, 56, in each power switch 48 are immediately turned off to preventing any current from conducting to the ground fault. The rapid switching of RB IGBTs 58, 56 extinguishes the ground fault current in microseconds. By contrast, prior art circuit breaker mechanisms take approximately 40 milliseconds to interrupt the ground fault current.
Referring next to
Active converter 32 ground fault protection eliminates the need for an input circuit breaker equipped with ground fault protection, or with other electro-mechanical means to process the input power. Active converter 64 configuration allows for the use of power fuses rather than more costly circuit breakers to feed the power to the input converter of a VSD, while retaining the ground fault protection feature. Fuses provide a significant reduction in the let-thru energy associated with a line-to-line fault that may occur within the VSD or filter, thereby reducing instances of the semi-conductor package rupture, or of other significant damage incurred in the case of a fault. By utilizing high speed fuses for the power feed, the arc-flash rating of the equipment (see, e.g., the National Fire and Protection Agency (NFPA) regulation 70E) can be significantly reduced. The high-speed fuses reduce the hazard associated with installing, maintaining and repairing the system. By replacing main circuit breakers with fuses at the input of the active converter, the system can interrupt higher levels of fault current, thus enabling the use of fused-input equipment on much lower impedance mains supplies. Active converter 64 significantly reduces the energy associated with clearing the ground fault, because semiconductors and controls can detect and extinguish the ground current flow in several microseconds, as contrasted with several tens of milliseconds for conventional topologies. The rapid response of the fuses minimizes ancillary damage associated with a ground fault. This advantage may be particularly apparent when used in HVAC&R applications where hermetic motors are employed. A ground fault occurring in the stator winding of a hermetic motor can cause significant and costly damage to the entire refrigeration circuit. Limiting the ground fault current that can flow in the stator limits collateral damage to other components of the HVAC&R system.
While only certain features and embodiments of the invention have been illustrated and described, many modifications and changes may occur to those skilled in the art (For example, variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (For example, temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (For example, those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.
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|U.S. Classification||361/42, 324/544, 324/509, 324/508, 361/1, 324/551, 318/563, 324/541, 361/31|
|Cooperative Classification||H02M1/32, H02H7/1216, H02M5/458|
|European Classification||H02H7/12D, H02M1/32, H02M5/458|
|Sep 5, 2008||AS||Assignment|
Owner name: JOHNSON CONTROLS TECHNOLOGY COMPANY, MICHIGAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SCHNETZKA, HAROLD R.;REEL/FRAME:021486/0513
Effective date: 20080416
|Apr 3, 2015||REMI||Maintenance fee reminder mailed|
|Aug 23, 2015||LAPS||Lapse for failure to pay maintenance fees|
|Oct 13, 2015||FP||Expired due to failure to pay maintenance fee|
Effective date: 20150823